Drug hypersensitivity reactions (DHRs) are a matter of great concern, both for outpatient and in hospital care. The evaluation of these patients is complex, because in vivo tests have a suboptimal sensitivity and can be time-consuming, expensive and potentially risky, especially drug provocation tests. There are several currently available in vitro methods that can be classified into two main groups: those that help to characterize the active phase of the reaction and those that help to identify the culprit drug. The utility of these in vitro methods depends on the mechanisms involved, meaning that they cannot be used for the evaluation of all types of DHRs. Moreover, their effectiveness has not been defined by a consensus agreement between experts in the field. Thus, the European Network on Drug Allergy and Drug Allergy Interest Group of the European Academy of Allergy and Clinical Immunology has organized a task force to provide data and recommendations regarding the available in vitro methods for DHR diagnosis. We have found that although there are many in vitro tests, few of them can be given a recommendation of grade B or above mainly because there is a lack of well-controlled studies, most information comes from small studies with few subjects and results are not always confirmed in later studies. Therefore, it is necessary to validate the currently available in vitro tests in a large series of well-characterized patients with DHR and to develop new tests for diagnosis.

The basophil activation test (BAT) has become a pervasive test for allergic response through the development of flow cytometry, discovery of activation markers such as CD63 and unique markers identifying basophil granulocytes. Basophil activation test measures basophil response to allergen cross-linking IgE on between 150 and 2000 basophil granulocytes in <0.1 ml fresh blood. Dichotomous activation is assessed as the fraction of reacting basophils. In addition to clinical history, skin prick test, and specific IgE determination, BAT can be a part of the diagnostic evaluation of patients with food-, insect venom-, and drug allergy and chronic urticaria. It may be helpful in determining the clinically relevant allergen. Basophil sensitivity may be used to monitor patients on allergen immunotherapy, anti-IgE treatment or in the natural resolution of allergy. Basophil activation test may use fewer resources and be more reproducible than challenge testing. As it is less stressful for the patient and avoids severe allergic reactions, BAT ought to precede challenge testing. An important next step is to standardize BAT and make it available in diagnostic laboratories. The nature of basophil activation as an ex vivo challenge makes it a multifaceted and promising tool for the allergist. In this EAACI task force position paper, we provide an overview of the practical and technical details as well as the clinical utility of BAT in diagnosis and management of allergic diseases.

Background: Quinolone hypersensitivity reactions are being more frequently reported. Skin tests in investigations of patients are known to not be fully reliable. The provocation test thus remains the gold standard in the definitive diagnosis of allergy, despite the risks involved. The aim of this study was to evaluate basophil activation tests (BATs) in the diagnosis of immediate-type reactions to quinolones. Methods: Thirty-four patients who presented an immediate-type hypersensivity reaction less than an hour after quinolone administration were studied. The allergologic workup of these patients consisted of a careful clinical history, a skin test and a BAT with the culprit quinolone. If not contraindicated, and in the case of high probability of a nonallergic reaction, provocation tests were performed to assess the nonimmunologic nature of the hypersensitivity. Results: Among the 34 patients studied, 17 (50%) presented a negative BAT to the suspected quinolone, while the other 17 (50%) patients presented a positive BAT for quinolone at the time of their reaction. Among the 17 patients with negative BATs, 15 (2 of whom had had positive skin tests) had quinolone successfully reintroduced. Conclusions: Our report suggests that the BAT, if negative for the culprit quinolone, is a valuable tool in the decision whether or not to perform provocation tests in patients with a history of immediate-type reaction to quinolones, in order to exclude an allergic reaction.

The role of T cells in contact hypersensitivity (CHS) to haptens has been well described. However, recent reports demonstrated that CHS-like reactions to experimental haptens could be induced in mice deficient in T cells and B cells, as a result of adaptive-like features of NK cells. Here, we compared hapten-specific inflammatory reactions induced by memory T cells or NK cells. Classical CHS protocols were applied to WT or T-and B-cell deficient mice. Adoptive transfers of hapten-specific T cells and NK cells were also performed. Liver NK cells from hapten-primed mice induced specific recall responses to haptens upon transfer in CD3e-deficient mice, thus confirming the existence of ''memory'' NK cells in the liver. We investigated the nature of the inflammation generated in these transfer conditions and found that hapten-induced skin inflammation mediated by CD8 1 T cells or ''memory'' NK cells are different. Indeed, ear swelling induced by memory NK cells was transient and not associated with cellular infiltrate and inflammation markers, characteristic for T-cell-mediated responses. Thus, NK cells and T cells mediate distinct forms of skin inflammation. NK cell-mediated pathogenesis does not rely on cellular infiltrate and could be involved in atypical forms of adverse drug reactions.